Add polygon drawing primitive (#314)

library/src/lib.rs

@@ -83,6 +83,7 @@ fn global(math: Module, calc: Module) -> Module {
     global.define("square", visualize::SquareElem::func());
     global.define("ellipse", visualize::EllipseElem::func());
     global.define("circle", visualize::CircleElem::func());
+    global.define("polygon", visualize::PolygonElem::func());
 
     // Meta.
     global.define("document", meta::DocumentElem::func());

library/src/visualize/mod.rs

@@ -3,7 +3,9 @@
 mod image;
 mod line;
 mod shape;
+mod polygon;
 
 pub use self::image::*;
 pub use self::line::*;
 pub use self::shape::*;
+pub use self::polygon::*;

library/src/visualize/polygon.rs

@@ -0,0 +1,71 @@
+use crate::prelude::*;
+
+/// A closed-path polygon.
+///
+/// ## Example
+/// ```example
+/// #polygon(fill: blue, (0pt, 0pt), (10pt, 0pt), (10pt, 10pt))
+/// ```
+///
+/// Display: Polygon
+/// Category: visualize
+#[element(Layout)]
+pub struct PolygonElem {
+    /// How to fill the polygon. See the
+    /// [rectangle's documentation]($func/rect.fill) for more details.
+    pub fill: Option<Paint>,
+
+    /// How to stroke the polygon. See the [lines's
+    /// documentation]($func/line.stroke) for more details.
+    #[resolve]
+    #[fold]
+    pub stroke: Option<PartialStroke>,
+
+    /// The vertices of the polygon. The polygon automatically closes itself.
+    #[variadic]
+    pub vertices: Vec<Axes<Rel<Length>>>,
+}
+
+impl Layout for PolygonElem {
+    fn layout(
+        &self,
+        _: &mut Vt,
+        styles: StyleChain,
+        regions: Regions,
+    ) -> SourceResult<Fragment> {
+        let points: Vec<Point> = self
+            .vertices()
+            .iter()
+            .map(|c| {
+                c.resolve(styles)
+                    .zip(regions.base())
+                    .map(|(l, b)| l.relative_to(b))
+                    .to_point()
+            })
+            .collect();
+
+        let size = points.iter().fold(Point::zero(), |max, c| c.max(max)).to_size();
+
+        let target = regions.expand.select(regions.size, size);
+        let mut frame = Frame::new(target);
+
+        // only create a path if there is more than zero points.
+        if points.len() > 0 {
+            let stroke = self.stroke(styles).map(|e| e.unwrap_or_default());
+            let fill = self.fill(styles);
+
+            // construct a closed path given all points.
+            let mut path = Path::new();
+            path.move_to(points[0]);
+            for point in &points[1..] {
+                path.line_to(*point);
+            }
+            path.close_path();
+
+            let shape = Shape { geometry: Geometry::Path(path), stroke, fill };
+            frame.push(Point::zero(), FrameItem::Shape(shape, self.span()));
+        }
+
+        Ok(Fragment::frame(frame))
+    }
+}

tests/typ/visualize/polygon.typ

@@ -0,0 +1,31 @@
+// Test polygons.
+
+---
+#set page(height: 220pt, width: 50pt)
+#box({
+  set polygon(stroke: 0.75pt, fill: blue)
+  polygon((0em, 0pt))
+  // this should not give an error
+  polygon()
+  polygon((0pt, 0pt), (10pt, 0pt))
+  polygon((5pt, 0pt), (0pt, 10pt), (10pt, 10pt))
+  polygon(
+    (0pt, 0pt), (5pt, 5pt), (10pt, 0pt),
+    (15pt, 5pt),
+    (5pt, 10pt)
+  )
+  polygon(stroke: none, (5pt, 0pt), (0pt, 10pt), (10pt, 10pt))
+  polygon(stroke: 3pt, fill: none, (5pt, 0pt), (0pt, 10pt), (10pt, 10pt))
+  // relative size
+  polygon((0pt, 0pt), (100%, 5pt), (50%, 10pt))
+  // antiparallelogram
+  polygon((0pt, 5pt), (5pt, 0pt), (0pt, 10pt), (5pt, 15pt))
+  // self-intersections
+  polygon((0pt, 10pt), (30pt, 20pt), (0pt, 30pt), (20pt, 0pt), (20pt, 35pt))
+})
+
+---
+// Test errors.
+
+// Error: 10-17 point array must contain exactly two entries
+#polygon((50pt,))